<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title>
    <style type="text/css">
*{margin: 0;padding: 0;list-style: none;}
html,body{
	height: 100%;
}
div{
	transition:.5s all ease;
}

    </style> 

    <link rel="stylesheet" type="text/css" href="css.css" media="(min-width:768px)">
    <link rel="stylesheet" type="text/css" href="css2.css" media="(min-width:320px) and (max-width:768px)">
</head>
<body>
	<div></div>
</body>
</html>